Vascular prosthesis, such as vascular grafts and stents, have been known for a number of years. Recently, it has been proposed that a helical formation formed on the internal surface of the vascular prosthesis can be used to generate desirable flow characteristics in blood flowing through the prosthesis, by encouraging spiral flow of the blood and so helping to reduce turbulence and/or dead spots with the fluid flow. It is believed that generating a spiral flow pattern in the blood, and thereby reducing turbulence and dead spots, can help to reduce vascular disease.
In this context, the term “spiral flow” refers to fluid flow in which there is a spiral and/or helical flow component to the fluid flow.
Examples of helical formations in vascular prosthesis are disclosed, for example, in International (PCT) Patent Application Nos. WO 00/38591 and WO 02/098325, and UK Patent Application No. 2369797 each of which is incorporated herein by reference.
However, one of the disadvantages of having a helical formation in a conduit is that the formation itself can create turbulence as the blood flows past the formation. This may have the unintentional effect of reducing or removing the spiral flow properties from the blood that the helical formation is intended to generate.